1. Field of the Invention
The present invention relates to a hot melt adhesive composition suitable for bonding and sealing between polycarbonate resins or acrylic resins, or between polycarbonate resins or acrylic resins and other materials in manufacturing lamps such as headlamps in automobiles, lighting, electronics parts, signals, etc., or in glazing side windows of automobiles and other windows. Particularly, the invention relates to a hot melt adhesive composition in which a staying phenomenon of foams at an adhered interface does not take place while maintaining adhesive force for a long period even if an adhered material is placed in an atmosphere of 80xc2x0 C. or higher after bonding.
2. Description of the Related Art
Polycarbonate resins have extremely high mechanical strength such as impact strength, thermal stability, superior electric properties, superior weatherability, and high transparency. Also, polycarbonate resins can be colored at will and are superior in size stability. For that reason, polycarbonate resins are used widely in machine parts, electric parts, electronic parts, lighting parts, household articles, etc.
For bonding or sealing of such polycarbonate resins, there has been employed a method in which a so-called hot melt adhesive such as ethylenevinyl acetate copolymer type or rubber type adhesives or sealing agent is introduced in an applicator and then melted, and the molten adhesive is applied to a polycarbonate resinous products to bond the resinous products together while the adhesive maintains stickiness.
However, when bonding or sealing of polycarbonate resins or bonding of the resins to other materials is carried out by using those conventional hot melt adhesives and thereafter the adhered product is heated at a temperature equal to or above 70xc2x0 C., low molecular weight compounds such as water and carbon dioxide are produced from the polycarbonate resin, which stay as foams at the interface between the polycarbonate resin and the hot melt adhesives, causing decrease in adhesive force or sealing force of the adhesives. Similar phenomena are observed in the cases of acrylic resins.
For that reason, hot melt adhesives through which foams of low molecular weight compounds such as water and carbon dioxide can be easily passed have been developed, but their blocking effects against staying foams are not sufficient. In practice, the adhesives are used for bonding or sealing after polycarbonate resins or acrylic resins are heated and dried previously to remove the above-mentioned low molecular weight compounds. It is desired, however, to avoid the previous heating and drying steps and decrease costs of equipment and processing.
In view of the above, the present inventors have proposed adhesive compositions for preventing foams to stay at the interface by blending a terpenebisphenol A copolymer as a tackifier with rubber (Japanese Patent Nos. 2763076 and 2779024). These adhesive compositions do have effects to a certain extent, but recently there are some cases requiring thermal resistance against a temperature equal to or above 80xc2x0 C. Therefore, an object of the present invention is to provide a hot melt adhesive composition with which no foam is remained at an adhered interface between a polycarbonate resin or an acrylic resin and the hot melt adhesive even if an adhered material is placed in an atmosphere of 80xc2x0 C. or higher after bonding without any decrease in adhesive force or sealing force of the adhesive.
The present invention directs the attention to water absorbability and carbon dioxide absorbability of calcium oxide to solve the above-mentioned problem.
That is, according to the present invention, there is provided a hot melt adhesive composition characterized in that 2-30 parts by mass of calcium oxide is blended with 100 parts by mass of a hot melt adhesive composition containing rubber, amorphous polyolefin and a resinous tackifier.
The hot melt adhesive composition according to the present invention preferably contains butyl rubber and a styrenediene type block copolymer as rubber components.
For the hot melt adhesive composition according to the present invention, a mass ratio of the styrenediene type block copolymer contained in the rubber components is preferably 5-40%.
For the hot melt adhesive composition according to the present invention, it is preferable to blend 25-100 parts by mass of amorphous polyolefin with 100 parts by mass of rubber.
For the hot melt adhesive composition according to the present invention, it is preferable to blend 50-200 parts by mass of a resinous tackifier with 100 parts by mass of rubber.
For the hot melt adhesive composition according to the present invention, the resinous tackifier is, preferably, at least one kind of resin selected from the group consisting of petroleum resins, terpene resins, modified products of these resins and hydrogenates of these resins.
For the hot melt adhesive composition according to the present invention, a mass ratio of the petroleum resins to the terpene type resins (terpene resin, modified terpene resin and hydrogenated terpene resins) is preferably 50/50-95/5.
The hot melt adhesive composition according to the present invention is preferably used for bonding with a polycarbonate resin or an acrylic resin.
The hot melt adhesive composition according to the present invention is preferably used for sealing between a lens of an automobile lamp made of a polycarbonate resin or an acrylic resin and a housing thereof.
Further, the present invention comprises an automobile lamp in which sealing is made between a lens made of a polycarbonate resin or an acrylic resin and a housing by using any one of the hot melt adhesive compositions stated above.